Self-expanding stent delivery system

ABSTRACT

A stent-delivery catheter system delivers and implants a self-expanding stent intraluminally into a human patient&#39;s body lumen. A self-expanding stent is removabaly attached to the distal end of an inner member so that attachment projections prevent axial movement of the stent on the inner member while the stent is being delivered and implanted in a patient&#39;s body lumen.

BACKGROUND OF THE INVENTION

The invention relates to self-expanding stent delivery systems, whichare used to implant a stent into a patient's body lumen to maintain thepatency thereof. The stent delivery system is useful in the treatmentand repair of body lumens, including coronary arteries, renal arteries,carotid arteries, and other body lumens.

Stents are generally cylindrically-shaped devices which function to holdopen and sometimes expand a segment of a blood vessel or other bodylumen. They are particularly suitable for use to support and hold back adissected arterial lining which can occlude the fluid passagewaytherethrough. Stents also are useful in maintaining the patency of abody lumen, such as a coronary artery, after a percutaneous transluminalcoronary angioplasty (PTCA) procedure or an atherectomy procedure toopen a stenosed area of the artery.

A variety of devices are known in the art for use as stents and haveincluded coiled wires in a variety of patterns that are expanded afterbeing placed intraluminally by a balloon catheter; helically wound coilsprings manufactured from an expandable heat sensitive material such asnickel-titanium; and self-expanding stents inserted in a compressedstate and shaped in a zig-zag pattern.

Typically, the aforementioned stents are delivered intraluminallythrough a percutaneous incision through the femoral or renal arteries. Astent is mounted on the distal end of an elongated catheter, typicallyon the balloon portion of a catheter, and the catheter and stent areadvanced intraluminally to the site where the stent is to be implanted.Typically with expandable stents, the balloon portion of the catheter isinflated to expand the stent radially outwardly into contact with thearterial wall, whereupon the stent undergoes plastic deformation andremains in an expanded state to hold open and support the artery.

With respect to self-expanding stents, typically a retractably sheath ispositioned over the self-expanding stent which is mounted on the distalend of the catheter. Once the catheter has been advanced intraluminallyto the site where the stent is to be implanted, the sheath is withdrawnthereby allowing the self-expanding stent to expand radially outwardlyinto contact with the arterial wall, thereby holding open and supportingthe artery.

One of the problems associated with the prior art stents andcatheter-delivery systems, is to removably attach the stent to thecatheter's distal end or the balloon portion of the catheter so that thestent does not dislodge or move axially on the catheter or balloon.

What has been needed and heretofore unavailable is a reliablecatheter-delivery system on which the stent can be mounted and removablyattached so that it does not move axially on the catheter either duringdelivery and advancement through the vascular system, or duringimplanting of the stent. The present invention satisfies this need.

SUMMARY OF THE INVENTION

The present invention is directed to a self-expanding stent deliverysystem in which a self-expanding stent is removably attached to acatheter so that the stent remains in position on the catheter until itis implanted. Unlike prior art stents, which may have a tendency todislodge or move axially on the catheter shaft when the sheath iswithdrawn or when the catheter is advanced through a tortuousvasculature, the present invention provides means for removablyattaching the stent to the catheter so that it cannot move axially onthe catheter shaft.

A catheter assembly for removably attaching an intravascular stent isprovided in which an elongated catheter has an inner member and an outermember extending along a longitudinal axis wherein the inner member andthe outer member have a coaxial configuration and are dimensioned forrelative axial movement. A self-expanding stent, having an open latticestructure, and being biased toward an open configuration, is mountedwithin the outer member. The inner member is slidably positioned withinthe lumen of the stent, and then the inner member is heated until itconforms and fills the open lattice structure of the stent withattachment projections.

The present invention includes an inner member that is naturally pliableand deformable or is heat-deformable and formed from a polymericmaterial which when heated will fill the open lattice structure of thestent with attachment projections. The inner member can be formed frompolymeric materials including polyurethanes, polyethylenes,polyethylterpthalate, and nylons.

In another embodiment of the invention, an elastomeric sleeve isattached to the distal end of the inner member. This stent is mounted inthe distal end of the outer member and is biased outwardly against theouter member. The inner member distal end and its sleeve are positionedwithin the stent, and the sleeve is heated until it fills and formsattachment projections in the open lattice structure of the stent.

The invention also relates to the method of mounting the self-expandingstent on the delivery catheter. The delivery catheter includes an outermember and an inner member having relative axial movement and controlhandles for providing relative axial movement between the members. Theself-expanding stent is positioned within the inner lumen of the outermember and the control handles are manipulated to slide the inner memberdistal end within the inner lumen of the self-expanding stent.Thereafter, heat is applied to the inner member distal end so that itconforms and fills the open lattice structure of the self-expandingstent with attachment projections, thereby removably attaching theself-expanding stent to the inner member distal end and preventing axialmovement of the stent. The self-expanding stent remains biased radiallyoutwardly and is retained from expanding by the outer member.

The invention also includes a method of implanting a self-expandingstent utilizing the catheter-delivery system described above. Using thecatheter-delivery system, the stent is advanced through a patient'svascular system until it is positioned at the site where the stent is tobe implanted. The control handles are manipulated to simultaneously movethe inner member axially in a distal direction and the outer memberaxially in a proximal direction. As the stent is exposed and no longerretained by the outer member, it will deploy by self-expanding radiallyoutwardly into contact with the body lumen. The stent will not moveaxially on the catheter shaft as the inner member and the outer memberare moved axially relative to one another, since the stent is removablyattached to the inner member by attachment projections. After the stentis deployed, the catheter-delivery system is withdrawn from the patient.

One feature of the present invention is to permit the physician topartially deploy the stent, and if it is improperly positioned, theouter member can be moved axially to recapture the partially deployedstent so that the stent can be repositioned in the proper location. Forexample, the control handles can be manipulated to simultaneously movethe inner member axially in the distal direction and the outer memberaxially in a proximal direction to begin to deploy the stent.Thereafter, if it is determined that the stent is being implanted at thewrong location in an artery, the control handles can be manipulated tosimultaneously move the inner member axially in a proximal direction andthe outer member axially in a distal direction to recapture thepartially deployed stent so that it can be repositioned in the properlocation in the artery. The stent is then implanted as described above.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the invention, whentaken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 represent elevational views of prior art stents andcatheter-delivery systems where the stents are self-expanding eitherbecause they are biased radially outwardly or formed from a heatsensitive material such as nickel-titanium.

FIG. 5 is a schematic view of the catheter-delivery system of theinvention having the self-expanding stent positioned within the innerlumen of the outer member before the stent is mounted on the innermember.

FIG. 5A is a cross section of FIG. 5 along line 5A-5A.

FIG. 6 is a schematic view depicting the inner member positioned withinthe inner lumen of the self-expanding stent, and a tapered mandrilinserted in the inner member for the purpose of applying heat to formattachment projections.

FIG. 7 is a schematic view depicting an alternative embodiment of theinvention in which an elastomeric segment is positioned on the distalend of the inner member and is used to conform and fill in the openlattice structure of the self-expanding stent with attachmentprojections.

FIG. 8 is a schematic view of an over-the-wire catheter-delivery systemin which the stent is being positioned at a narrowed portion of thevessel wall.

FIG. 9 is a schematic view depicting the over-the-wire catheter-deliverysystem of FIG. 8 in which the outer member is being withdrawn proximallyso that the stent can self-expand radially outwardly into contact withthe vessel wall.

FIG. 10 is a schematic view depicting the stent of FIGS. 8 and 9 beingimplanted and contacting the vessel wall.

FIG. 11 is a schematic view depicting a rapid-exchange catheter-deliverysystem in which the guide wire extends through a port in the side ofcatheter so that the catheter may be rapidly exchanged upon withdrawalfrom the patient.

FIG. 12 is a schematic view depicting the catheter-delivery system ofFIG. 11 in which the stent is self-expanding as the outer member iswithdrawn axially in the proximal direction.

FIG. 13 is a schematic view depicting the rapid-exchangecatheter-delivery system in which the self-expanding stent has beenimplanted into contact with the vessel wall, and the rapid-exchangecatheter is ready to be withdrawn from the patient's vascular system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a stent delivery catheter system inwhich a self-expanding stent is delivered intraluminally into a humanpatient's body lumen, such as a coronary artery, carotid artery, renalarteries, peripheral arteries and veins, and the like. The inventionprovides for a stent delivery catheter assembly and its method of use inwhich a stent is implanted in a patient.

As can be seen in FIGS. 1-4, there are numerous prior art stents whichare adapted for use with the present invention. The stents depicted inFIGS. 1-4 are all self-expanding stents and will expand from acontracted condition where they are mounted on the catheter assembly, toan expanded condition where the stent comes in contact with the bodylumen. The stents are self-expanding, which can be achieved by severalmeans. As depicted in FIGS. 1-4, the prior art stents are formed from astainless steel material and are configured so that they are biasedradially outwardly and they will expand outwardly unless restrained. Thestents depicted in FIGS. 1-4 also can be formed from a heat sensitivematerial, such as nickel titanium, which will self-expand radiallyoutwardly upon application of a transformation temperature. These priorart stents are representative of a large number of stents which can beadapted for use with the present invention.

In a preferred embodiment of the invention, as depicted in FIGS. 5, 5Aand 6, catheter assembly 20 is provided to deliver and implant a stent.Catheter assembly 20 incorporates elongated catheter body 21 which hasproximal end 22 and distal end 23. An inner member 24 and an outermember 25 are arranged in coaxial alignment. Inner member 24 is slidablypositioned within outer member 25 and relative axial movement betweenthe two members is provided by inner member control handle 26 and outermember control handle 27. The control handles 26,27 can take numerousforms, but are depicted schematically for ease of illustration. As anexample, however, control handles 26, 27 can take the form of athumb-switch arrangement, a rotating-screw-type arrangement, or aratcheting arrangement. Such control handle means are well known inprior art catheter-delivery systems.

A self-expanding stent 28 having an open lattice structure 29 is mountedon the distal end 23 of catheter assembly 20. Self-expanding stent 28can take virtually any configuration that has an open lattice structure29, as can be seen in the examples of the prior art stents shown inFIGS. 1-4.

In keeping with the invention, the self-expanding stent 28 is insertedin outer member inner lumen 31 and positioned at the outer member distalend. In those instances where self-expanding stent 28 is made fromstainless steel or a similar material that is biased outwardly, stent 28will be compressed and inserted into inner lumen 31. Thereafter, innermember distal end 32 is positioned within stent inner lumen 34 so thatthe inner member outer surface 33 can come into contact with the stentinner lumen 34.

In keeping with the preferred embodiment, inner member distal end 32 ismade from a polymeric material that either is soft by design, or willbecome soft when heat is applied. The intent is to removably attachself-expanding stent 28 on outer surface 33 of inner member 24. Outersurface 33 will partially fill the open lattice structure 29 of stent 28to form attachment projections 30 so that the stent cannot move in anaxial direction along outer surface 33 of inner member 24.

In the preferred embodiment, self-expanding stent 28 is mounted on outersurface 33 at the inner member distal end 32 and the open latticestructure 29 is filled by attachment projections 30. Due to the coaxialarrangement between inner member 24 and outer member 25, the inner lumen31 of outer member 25 covers self-expanding stent 28 and helps to retainthe stent on the outer surface 33 of the inner member 24.

In order to conform outer surface 33 so that it conforms or fills theopen lattice structure 29 of the self-expanding stent with attachmentprojections 30, heat can be applied by various methods. For example, atapered mandrill 35, as depicted in FIG. 6, is inserted in inner memberdistal end 32 in region of the stent. Heat is then applied to outermember 25 by known means, such as by using a heated capture tube (notshown) surrounding outer member 25. The capture tube can be formed fromteflon, glass, or the like and generally is warmed by using heated air.As outer member warms, inner member 33 is inserted within inner lumen 31of outer member 25 allowing attachment projections 30 to flow and formaround stent 28.

In another preferred embodiment, as depicted in FIG. 7, an elastomericsegment 40 is attached on outer surface 33 at the distal end 32 of theinner member. Elastomeric segment 40 is formed from a heat sensitivematerial, or is designed to be relatively soft as compared to innermember 24, such that stent 28 can be removably attached on elastomericsegment 40, which will conform and fill in open lattice structure 29 ofthe stent with attachment projections 30. The elastomeric segment can beheated by the aforementioned methods, or if it is formed of a materialthat is relatively soft, it will naturally conform and fill in openlattice structure 29 with attachment projections 30 without theapplication of heat.

In the preferred method of use, catheter assembly 20 is used to implantthe self-expanding stent in a body lumen using an over-the-wire orrapid-exchange catheter configuration. In one preferred embodiment, asdepicted in FIGS. 8-10, over-the-wire catheter 50 has a guide wire lumen51 which extends through the catheter and is configured to receive guidewire 52. In order to implant self-expanding stent 28, guide wire 52 ispositioned in a patient's body lumen, at vessel wall 55, and typicallyguide wire 52 extends past a stenosed region 56. Distal end 54 ofover-the-wire catheter 50 is threaded over the proximal end of the guidewire which is outside the patient (not shown) and catheter 50 isadvanced along the guide wire until distal end 54 of catheter 50 ispositioned within stenosed region 56.

As depicted in FIGS. 9 and 10, self-expanding stent 28 is implanted instenosed region 56 by moving outer member 25 in a proximal directionwhile simultaneously moving inner member 24 in a distal direction. Thestent 28 will not slide or move axially on outer surface 33 since theopen lattice structure is filled in with attachment projections 30. Asportions of self-expanding stent 28 are no longer contained by outermember 24, it will expand radially outwardly into contact with vesselwall 55 in the area of stenosed region 56. When fully deployed andimplanted, as shown in FIG. 10, stent 28 will support and hold openstenosed region 56 so that blood flow is not restricted. Attachmentprojections 30 do not inhibit the stent 28 from self-expanding radiallyoutwardly, they only impede axial movement of the stent.

With certain self-expanding stents, there is a tendency of the stent toshorten somewhat when it expands. When stent shortening occurs, thephysician may find that the stent has been improperly placed in thestenosed region 56 if the effects of shortening have not been taken intoconsideration. Accordingly, it may be necessary, as described above, tomove inner member 24 distally in order to compensate for stentshortening upon expansion of the stent. It is also possible due to stentdesign, that the self-expanding stent will not appreciably shorten uponexpansion. If this is the case, it may be unnecessary to move innermember 24 distally while simultaneously moving outer member 25proximally in order to release self-expanding stent 28 in the bodylumen. With a stent configuration that does not appreciably shortenduring expansion, outer member 25 is moved axially while inner member 24remains stationary as self-expanding stent 28 expands radially outwardlyinto contact with vessel wall 55. After stent 28 is implanted andcontacts stenosed region 56, over-the-wire catheter 50 is withdrawn fromthe patient's vascular system. A typical over-the-wire catheter designis disclosed in U.S. Pat. No. B1 4,323,071, which is incorporated hereinby reference.

In another preferred method of implanting a stent, as depicted in FIGS.11-13, rapid-exchange catheter 60 is provided. Rapid-exchange cathetersare known in the art and details of the construction and use are setforth in U.S. Pat. Nos. 5,458,613; 5,346,505; and 5,300,085, which areincorporated herein by reference. Generally, rapid-exchange cathetersinclude guide wire lumen 61 which extends in the distal portion of thecatheter from side port 63 to the distal end of the catheter. Guide wire62 is inserted through guide port 63 and extends out the distal end ofcatheter 60 so that the distal end of the guide wire is positionedbeyond stenosed region 56. The method of deploying self-expanding stent28 using rapid-exchange catheter 60 is similar to that described forusing over-the-wire catheter 50. One of the differences between thecatheter-delivery systems includes slit 64 in rapid-exchange catheter 60which extends from side port 63 to approximately just proximal of thearea where stent 28 is mounted. After stent 28 is implanted in stenosedregion 56, rapid-exchange catheter 60 is withdrawn from the patient'svascular system and guide wire 62 will peel through slit 64 making theexchange of one catheter for another a simple process. Typically,stiffening mandrill 65 is incorporated in the proximal region ofrapid-exchange catheter 60 to enhance the pushability of the catheterthrough the patient's vascular system, and to improve the trackabilityof the catheter over the guide wire.

The stents as described herein can be formed from any number ofmaterials, including metals, metal alloys and polymeric materials.Preferably, the stents are formed from metal alloys such as stainlesssteel, tantalum, or the so-called heat sensitive metal alloys such asnickel titanium (NiTi). Stents formed from stainless steel or similaralloys typically are designed, such as in a helical coil or the like, sothat they are spring biased outwardly.

With respect to stents formed from shape-memory alloys such as NiTi(nickel-titanium alloy), the stent will remain passive in itsmartensitic state when it is kept at a temperature below the transitiontemperature. In this case, the transition temperature will be belownormal body temperature, or about 98.6° F. When the NiTi stent isexposed to normal body temperature, it will immediately attempt toreturn to its austenitic state, and will rapidly expand radiallyoutwardly to achieve its preformed state. Details relating to theproperties of devices made from nickel-titanium can be found in"Shape-Memory Alloys," Scientific American, Vol. 281, pages 74-82(November 1979), which is incorporated herein by reference.

With respect to all of the embodiments disclosed above, inner member 24,and for that matter outer member 25, can be formed from polymericmaterials including polyurethanes, polyethylenes, polyethylterpthalate,and nylons. Similarly, elastomeric segment 40 can be formed frompolyurethane, elastomeric polyesters and the like. Generally speaking,the more proximal portions of inner member 24 and outer member 25 willbe formed of a polymeric material that is stiffer than the distalsection so that the proximal section has sufficient pushability toadvance through the patient's vascular system. On the other hand, themore distal portion of inner member 24 and outer member 25 can be formedof a more flexible material so that the distal portion of the catheterwill remain flexible and track more easily over the guide wire.

Other modifications and improvements may be made without departing fromthe scope of the invention. For example, the various drawing figuresdepict several configurations of the stent including various sizes,which can be modified to suit a particular application without departingfrom the spirit and scope of the invention. Further, the configurationof the catheter assembly is a coaxial arrangement between the innermember and the outer member, which can be modified to otherconfigurations without departing from the preferred invention.

What is claimed is:
 1. A catheter assembly comprising:an elongatedcatheter having a proximal end and a distal end; the catheter having aninner member and an outer member extending along a longitudinal axis,the inner member and the outer member having a coaxial configuration anddimensioned for relative axial movement; means for providing relativeaxial movement between the inner member and the outer member; aself-expanding stent having an open lattice structure configured to bebiased from a delivery configuration having a reduced cross section anda predetermined length to an open configuration with an enlarged crosssection and being positioned within a distal end of the outer member inthe delivery configuration; and a plurality of attachment projections ata distal end of the inner member spaced along the stent a distance atleast as great as the predetermined length for facilitating theremovable attachment of the stent to the inner member distal end.
 2. Thecatheter assembly of claim 1, wherein the attachment projections areformed from a heat-deformable polymeric material at the distal end ofthe inner member.
 3. The catheter assembly of claim 2, wherein thepolymeric material on the distal end of the inner member is taken fromthe group of polymeric materials including polyurethanes, polyethylenes,polyethylterpthalate, and nylons.
 4. The catheter assembly of claim 1,wherein the means for providing relative axial movement between theinner member and the outer member includes a control handle positionedat the proximal end of the elongated catheter.
 5. The catheter assemblyof claim 1, wherein the self-expanding stent is formed from a metalalloy taken from the group of metal alloys including stainless steel,nickel-titanium, and tantalum.
 6. The catheter assembly of claim 1,wherein the inner member of the elongated catheter has a through lumenfor receiving a guide wire so that the elongated catheter can bepositioned within a body lumen by advancing it over the guide wire. 7.The catheter assembly of claim 1, wherein the inner member of theelongated catheter has a side port for receiving a guide wire, the sideport being positioned so that the catheter can be rapidly exchanged. 8.The catheter assembly of claim 1, wherein the distal end of theelongated catheter includes an elastomeric sleeve attached to the distalend, the elastomeric sleeve adapted to conform and fill the latticestructure of the self-expanding stent with the plurality of attachmentprojections.
 9. A method of mounting an intravascular stent on adelivery catheter, the method comprising:providing a delivery catheterhaving an elongated catheter body and a proximal end and a distal end,the catheter having an inner member and an outer member extending alonga longitudinal axis, the inner member and the outer member having acoaxial configuration and dimensioned for relative axial movement, andcontrol handles for providing relative axial movement between the innermember and the outer member; positioning a self-expanding stent in adelivery configuration having an open lattice structure a reduced crosssection and a predetermined length within an inner lumen of the outermember; manipulating the control handles to slide the inner memberdistal end within an inner lumen of the self-expanding stent; andheating the inner member distal end so that it conforms and fills theopen lattice structure of the self-expanding stent with a plurality ofattachment projections spaced along the stent a distance at least asgreat as the predetermined length thereby removably attaching theself-expanding stent to the inner member distal end.
 10. A method ofimplanting a self-expanding stent in a body lumen, the methodcomprising:providing an elongated catheter having a proximal end and adistal end, the catheter having an inner member and an outer memberextending along a longitudinal axis, the inner member and the outermember having a coaxial configuration and dimensioned for relative axialmovement, the inner member distal end encircled by a self-expandingstent in a delivery configuration having a reduced cross section and apredetermined length, the inner member capable of being heated wherebyit conforms and fills an open lattice structure of the self-expandingstent with a plurality of attachment projections, the projections spacedalong the stent a distance at least as great as the predeterminedlength, control handles for providing relative axial movement betweenthe inner member and the outer member, and the distal end of the outermember forming a sheath around the self-expanding stent; manipulatingthe control handles to simultaneously move the inner member axially in adistal direction and the outer member axially in a proximal direction;deploying the stent by permitting it to self-expand radially outwardlyinto contact with the body lumen while preventing axial movement of thestent on the catheter by a plurality of the attachment projections; andwithdrawing the catheter from the body lumen.
 11. The method ofimplanting a stent of claim 10, the method further comprising thedeploying and withdrawing steps further including:positioning the distalend of the catheter at the site for implanting the stent; manipulatingthe control handles to simultaneously move the inner member axially in adistal direction and the outer member axially in a proximal direction tobegin implanting the stent; manipulating the control handles tosimultaneously move the inner member axially in a proximal direction andthe outer member axially in a distal direction to recapture the stentand to position the stent on the inner member distal end; repositioningthe catheter distal end to implant the stent; manipulating the controlhandles to simultaneously move the inner member axially in a distaldirection and the outer member axially in the proximal direction torelease the stent to self-expand in the body lumen; and withdrawing thecatheter from the body lumen.
 12. A method of implanting aself-expanding stent in a body lumen, the method comprising:providing anelongated catheter having a proximal end and a distal end, the catheterhaving an inner member and an outer member extending along alongitudinal axis, the inner member and the outer member having acoaxial configuration and dimensioned for relative axial movement, theinner member distal end encircled by a self-expanding stent in adelivery configuration having an open lattice structure, a reduced crosssection and a predetermined length, the inner member capable of beingheated whereby it conforms and fills the open lattice structure of theself-expanding stent with a plurality of attachment projections, theprojections spaced along the stent a distance at least as great as thepredetermined length, control handles for providing relative axialmovement between the inner member and the outer member, the distal endof the outer member forming a sheath around the self-expanding stent;manipulating the control handles to move the outer member axially in aproximal direction while maintaining the inner member stationary;deploying the stent by permitting it to self-expand radially outwardlyinto contact with the body lumen; and withdrawing the catheter from thebody lumen.
 13. The method of implanting a stent of claim 12, the methodfurther comprising, prior to said withdrawing step:positioning thedistal end of the catheter at the site for implanting the stent;manipulating the control handles to simultaneously move the inner memberaxially in a proximal direction and the outer member axially in a distaldirection to recapture the stent; repositioning the catheter distal endto implant the stent; manipulating the control handles to move the outermember axially in the proximal direction to release the stent toself-expand in the body lumen while simultaneously holding the innermember stationary; and withdrawing the catheter from the body lumen.